I have tried the cassette adapters, and found the sound qaulity horrible. I used the iRock, but the battery life was dismal, and with only 4 staion possibilities it was easy to get somewhere there was always overlap with commerical radie. I used the Griffin iTune and thought it worked well, but changin frequency was difficult as you drove down teh road. I have the Monster cable now, and it works OK. I use the Alpine system in my TJ and am extremly happy with it. I know Kenwood has one and Pioneer now, but both do not seem as nice as the Alpine system
There are a few choices to wire to factory HU, and I here these are expensive, but work well.